Thia(dia)zoles as fast dissociating dopamine 2 receptor antagonists

ABSTRACT

The present invention relates to [1-(benzyl)-piperidin-4-yl]-([1,3,4]thiadiazol-2-yl)-amine and [1-(benzyl)-piperidin-4-yl]-(thiazol-2-yl)-amine derivatives of formula (I) that are fast dissociating dopamine 2 receptor antagonists, processes for preparing these compounds, pharmaceutical compositions comprising these compounds as an active ingredient. The compounds find utility as medicines for treating or preventing central nervous system disorders, for example schizophrenia, by exerting an antipsychotic effect without motor side effects.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from and is the national stage of PCT Application No. PCT/EP2008/054732, filed Apr. 18, 2008, which claims priority from European Patent Application No. 07106706.0, filed Apr. 23, 2007, the entire disclosures of which are hereby incorporated in their entirety.

FIELD OF THE INVENTION

The present invention relates to [1-(benzyl)-piperidin-4-yl]-([1,3,4]thiadiazol-2-yl)-amine and [1-(benzyl)-piperidin-4-yl]-(thiazol-2-yl)-amine derivatives that are fast dissociating dopamine 2 receptor antagonists, processes for preparing these compounds, pharmaceutical compositions comprising these compounds as an active ingredient. The compounds find utility as medicines for treating or preventing central nervous system disorders, for example schizophrenia, by exerting an antipsychotic effect without motor side effects.

DESCRIPTION OF THE INVENTION

Schizophrenia is a severe and chronic mental illness that affects approximately 1% of the population. Clinical symptoms are apparent relatively early in life, generally emerging during adolescence or early adulthood. The symptoms of schizophrenia are usually divided into those described as positive, including hallucinations, delusions and disorganised thoughts and those referred to as negative, which include social withdrawal, diminished affect, poverty of speech and the inability to experience pleasure. In addition, schizophrenic patients are suffering from cognitive deficits, such as impaired attention and memory. The aetiology of the disease is still unknown, but aberrant neurotransmitter actions have been hypothesized to underlie the symptoms of schizophrenia. The dopaminergic hypothesis is one most often considered; it proposes that hyperactivity of dopamine transmission is responsible for the positive symptoms observed in schizophrenic patients. This hypothesis is based on the observation that dopamine enhancing drugs, such as amphetamine or cocaine, may induce psychosis, and on the correlation that exists between clinical doses of antipsychotics and their potency in blocking dopamine D2 receptors. All marketed antipsychotics mediate their therapeutic efficacy against positive symptoms by blocking the dopamine D2 receptor. Apart from the clinical efficacy, it appears that the major side effects of antipsychotics, such as extrapyramidal symptoms (EPS) and tardive dyskinesia, are also related to dopamine antagonism. Those debilitating side effects appear most frequently with the typical or first generation of antipsychotic (e.g., haloperidol). They are less pronounced with the atypical or second generation of antipsychotic (e.g., risperidone, olanzapine) and even virtually absent with clozapine, which is considered the prototypical atypical antipsychotic. Among the different theories proposed for explaining the lower incidence of EPS observed with atypical antipsychotics, the one that has caught a lot of attention during the last fifteen years, is the multireceptor hypothesis. It follows from receptor binding studies showing that many atypical antipsychotics interact with various other neurotransmitter receptors in addition to dopamine D2 receptors, in particular with the serotonin 5-HT2 receptors, whereas typical antipsychotic like haloperidol bind more selectively to the D2 receptors. This theory has been challenged in recent years because all major atypical antipsychotics fully occupy the serotonin 5-HT2 receptors at clinically relevant dosages but still differ in inducing motor side-effects. As an alternative to the multireceptor hypothesis, Kapur and Seeman (“Does fast dissociation from the dopamine D2 receptor explain the action of atypical antipsychotics?: A new hypothesis”, Am. J. Psychiatry 2001, 158:3 p. 360-369) have proposed that atypical antipsychotics can be distinguished from typical antipsychotics by the rates at which they dissociate from dopamine D2 receptors. The fast dissociation from the D2 receptor would make an antipsychotic more accommodating of physiological dopamine transmission, permitting an antipsychotic effect without motor side effects. This hypothesis is particularly convincing when one considers clozapine and quetiapine. These two drugs have the fastest rate of dissociation from dopamine D2 receptors and they carry the lowest risk of inducing EPS in humans. Conversely, typical antipsychotics associated with a high prevalence of EPS, are the slowest dissociating dopamine D2 receptor antagonists. Therefore, identifying new drugs based on their rate of dissociation from the D2 receptor appears as a valid strategy to provide new atypical antipsychotics. An additional goal is to combine fast dissociating properties with selectivity for dopamine D2 receptors. The multiple receptor profile of current atypical antipsychotics is thought to be the cause of other side effects, such as weight gain and diabetes. Searching for selective D2 antagonists has been ignored as an approach for some time but it is our belief that using more selective compounds in clinic may reduce the occurrence of metabolic disorders associated with current atypical antipsychotic drugs.

It is the object of the present invention to provide novel compounds that are fast dissociating dopamine 2 receptor antagonists which have an advantageous pharmacological profile as explained hereinbefore, in particular reduced motor side effects, and moderate or negligible interactions with other receptors resulting in reduced risk of developing metabolic disorders.

This goal is achieved by the present novel compounds according to Formula (I):

the pharmaceutically acceptable salts and solvates thereof, and stereoisomeric forms thereof, wherein

-   -   R is hydrogen or C₁₋₆alkyl;     -   R¹ is phenyl; phenyl substituted with 1, 2 or 3 substituents         each independently selected from the group consisting of halo,         cyano, C₁₋₄alkyl, C₁₋₄alkyloxy, perfluoroC₁₋₄alkyl, and         perfluoroC₁₋₄alkyloxy; thienyl; thienyl substituted with 1 or 2         substituents selected from the group consisting of halo and         C₁₋₄alkyl; C₁₋₄alkyl; or C₁₋₄alkyl substituted with hydroxyl,         C₃₋₈cycloalkyl or C₅₋₇cycloalkenyl;     -   R² is hydrogen or C₁₋₆alkyl;     -   R³ is hydrogen, trifluoromethyl or cyano; and     -   X is N or CR⁴ wherein R⁴ is hydrogen, trifluoromethyl or cyano.

The compounds according to the invention are fast dissociating D₂ receptor antagonists. This property renders the compounds according to the invention especially suitable for use as a medicine in the treatment or prevention of schizophrenia, schizophreniform disorder, schizoaffective disorder, delusional disorder, brief psychotic disorder, shared psychotic disorder, psychotic disorder due to a general medical condition, substance-induced psychotic disorder, psychotic disorder not otherwise specified; psychosis associated with dementia; major depressive disorder, dysthymic disorder, premenstrual dysphoric disorder, depressive disorder not otherwise specified, Bipolar I disorder, bipolar II disorder, cyclothymic disorder, bipolar disorder not otherwise specified, mood disorder due to a general medical condition, substance-induced mood disorder, mood disorder not otherwise specified; generalized anxiety disorder, obsessive-compulsive disorder, panic disorder, acute stress disorder, post-traumatic stress disorder; mental retardation; pervasive developmental disorders; attention deficit disorders, attention-deficit/hyperactivity disorder, disruptive behaviour disorders; personality disorder of the paranoid type, personality disorder of the schizoid type, personality disorder of the schizotypical type; tic disorders, Tourette's syndrome; substance dependence; substance abuse; substance withdrawal; trichotillomania.

A person skilled in the art can make a selection of compounds based on the experimental data provided in the Experimental Part hereinafter. Any selection of compounds is embraced within this invention.

A first group of compounds relates to compounds of Formula (I) and stereoisomeric forms thereof, wherein

R is hydrogen;

R¹ is phenyl; phenyl substituted with 1, 2 or 3 substituents each independently selected from the group consisting of hydrogen, halo, cyano, C₁₋₄alkyl, C₁₋₄alkyloxy, perfluoroC₁₋₄alkyl, and trifluoromethoxy; thienyl; thienyl substituted with 1 or 2 substituents selected from the group consisting of halo and C₁₋₄alkyl; C₁₋₄alkyl; C₁₋₄alkyl substituted with hydroxyl, C₃₋₈cycloalkyl or C₅₋₇cycloalkenyl; R² is hydrogen or methyl; X is nitrogen and R³ is trifluoromethyl.

A second group of compounds relates to compounds of Formula (I) and stereoisomeric forms thereof, wherein

R is hydrogen;

R¹ is phenyl; phenyl substituted with 1, 2 or 3 substituents each independently selected from the group consisting of hydrogen, halo, cyano, C₁₋₄alkyl, C₁₋₄alkyloxy, perfluoroC₁₋₄alkyl, and trifluoromethoxy; thienyl; thienyl substituted with 1 or 2 substituents selected from the group consisting of halo and C₁₋₄alkyl; C₁₋₄alkyl; or C₁₋₄alkyl substituted with hydroxyl, C₃₋₈cycloalkyl or C₅₋₇cycloalkenyl; R² is hydrogen or methyl; X is nitrogen and R³ is cyano.

A third group of compounds relates to compounds of Formula (I) and stereoisomeric forms thereof, wherein

R is hydrogen;

R¹ is phenyl; phenyl substituted with 1, 2 or 3 substituents each independently selected from the group consisting of hydrogen, halo, cyano, C₁₋₄alkyl, C₁₋₄alkyloxy, perfluoroC₁₋₄alkyl, and trifluoromethoxy; thienyl; thienyl substituted with 1 or 2 substituents selected from the group consisting of halo and C₁₋₄alkyl; C₁₋₄alkyl; or C₁₋₄alkyl substituted with hydroxyl, C₃₋₈cycloalkyl or C₅₋₇cycloalkenyl; R² is hydrogen or methyl; R³ is hydrogen; and X is CR4 wherein R⁴ is trifluoromethyl.

Amongst the compounds of Formula (I) and the stereoisomeric forms thereof, the most interesting are, for example,

-   [1-(4-Fluoro-benzyl)-piperidin-4-yl]-methyl-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine     (E1), -   [1-(3-Fluoro-benzyl)-piperidin-4-yl]-methyl-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine     (E2), -   [1-(4-Fluoro-benzyl)-piperidin-4-yl]-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine     (E4), -   [1-(3,4-Difluoro-benzyl)-piperidin-4-yl]-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine     (E5), -   [1-(3-Fluoro-4-methyl-benzyl)-piperidin-4-yl]-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine     (E9), -   1-(3-Fluoro-4-trifluoromethyl-benzyl)-piperidin-4-yl]-(5-trifluoromethyl-[1,3,4]thiadiazo-2-yl)-amine     (E10), -   [1-(3-Trifluoromethoxy-benzyl)-piperidin-4-yl]-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine     (E13), -   5-[1-(3-Trifluoromethyl-benzyl)-piperidin-4-ylamino]-[1,3,4]thiadiazole-2-carbonitrile     (E17), -   5-[1-(3-Fluoro-5-trifluoromethyl-benzyl)-piperidin-4-ylamino]-[1,3,4]thiadiazole-2-carbonitrile     (E18), -   5-[1-(3,4-Difluoro-benzyl)-piperidin-4-ylamino]-[1,3,4]thiadiazole-2-carbonitrile     (E19), -   5-[1-(3,4,5-Trifluoro-benzyl)-piperidin-4-ylamino]-[1,3,4]thiadiazole-2-carbonitrile     (E21), -   [1-(3,4-Difluoro-benzyl)-piperidin-4-yl]-(4-trifluoromethylthiazol-2-yl)-amine     (E22) -   (1-Benzyl-piperidin-4-yl)-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine     (D3) and -   (1-Benzyl-piperidin-4-yl)-(4-trifluoromethylthiazol-2-yl)-amine     (D8).

Throughout this application, the term “C₁₋₄alkyl” when used alone and when used in combinations such as “C₁₋₄alkyloxy”, “perfluoroC₁₋₄alkyl”, “diC₁₋₄alkylamino”, includes, for example, methyl, ethyl, propyl, butyl, 1-methylpropyl, 1,1-dimethylethyl, the term; “perfluoroC₁₋₄alkyl” includes for example trifluoromethyl, pentafluoroethyl, heptafluoropropyl and nonafluorobutyl; “C₃₋₈cycloalkyl” includes cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl; “C₅₋₇cycloalkenyl” includes cyclopentenyl, cyclohexenyl and cycloheptenyl. The term halo includes fluoro, chloro, bromo, and iodo.

The pharmaceutically acceptable salts are defined to comprise the therapeutically active non-toxic acid addition salts forms that the compounds according to Formula (I) are able to form. Said salts can be obtained by treating the base form of the compounds according to Formula (I) with appropriate acids, for example inorganic acids, for example hydrohalic acid, in particular hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid and phosphoric acid; organic acids, for example acetic acid, hydroxyacetic acid, propanoic acid, lactic acid, pyruvic acid, oxalic acid, malonic acid, succinic acid, maleic acid, mandelic acid, fumaric acid, malic acid, tartaric acid, citric acid, methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, cyclamic acid, salicylic acid, p-aminosalicylic acid, pamoic acid and mandelic acid. Conversely, said salts forms can be converted into the free forms by treatment with an appropriate base.

The term solvates refers to hydrates and alcoholates which the compounds of Formula (I) may form.

The term “stereochemically isomeric forms” as used hereinbefore defines all the possible isomeric forms that the compounds of Formula (I) may possess. Unless otherwise mentioned or indicated, the chemical designation of compounds denotes the mixture of all possible stereochemically isomeric forms, said mixtures containing all diastereomers and enantiomers of the basic molecular structure. More in particular, stereogenic centers may have the R- or S-configuration; substituents on bivalent cyclic (partially) saturated radicals may have either the cis- or trans-configuration. Compounds encompassing double bonds can have an E or Z-stereochemistry at said double bond. Stereochemically isomeric forms of the compounds of Formula (I) are embraced within the scope of this invention.

The compounds of Formula (I) as prepared in the processes described below may be synthesized in the form of racemic mixtures of enantiomers that can be separated from one another following art-known resolution procedures. The racemic compounds of Formula (I) may be converted into the corresponding diastereomeric salt forms by reaction with a suitable chiral acid. Said diastereomeric salt forms are subsequently separated, for example, by selective or fractional crystallization and the enantiomers are liberated therefrom by alkali. An alternative manner of separating the enantiomeric forms of the compounds of Formula (I) involves liquid chromatography using a chiral stationary phase. Said pure stereochemically isomeric forms may also be derived from the corresponding pure stereochemically isomeric forms of the appropriate starting materials, provided that the reaction occurs stereospecifically. Preferably if a specific stereoisomer is desired, said compound would be synthesized by stereospecific methods of preparation. These methods will advantageously employ enantiomerically pure starting materials.

Pharmacology

In order to find antipsychotic compounds active against positive symptoms and having an improved safety profile (low EPS incidence and no metabolic disorders), we have screened for compounds selectively interacting with the dopamine D2 receptor and dissociating fast from this receptor. Compounds were first screened for their D2 affinity in a binding assay using [³H]spiperone and human D2L receptor cell membranes. The compounds showing an IC₅₀ less than 10 μM were tested in an indirect assay adapted from a method published by Josee E. Leysen and Walter Gommeren, Journal of Receptor Research, 1984, 4(7), 817-845, to evaluate their rate of dissociation.

The compounds were further screened in a panel of more than 50 common G-protein coupled receptors (CEREP) and found to have a clean profile, that is to have low affinity for the tested receptors.

Some of the compounds have been further tested in in vivo models such as the “Antagonism of apomorphine induced agitation test in rats” and found to be orally active and bio-available.

In view of the aforementioned pharmacology of the compounds of Formula (I), it follows that they are suitable for use as a medicine, in particular for use as an antipsychotic. More especially the compounds are suitable for use as a medicine in the treatment or prevention of schizophrenia, schizophreniform disorder, schizoaffective disorder, delusional disorder, brief psychotic disorder, shared psychotic disorder, psychotic disorder due to a general medical condition, substance-induced psychotic disorder, psychotic disorder not otherwise specified; psychosis associated with dementia; major depressive disorder, dysthymic disorder, premenstrual dysphoric disorder, depressive disorder not otherwise specified, Bipolar I disorder, bipolar II disorder, cyclothymic disorder, bipolar disorder not otherwise specified, mood disorder due to a general medical condition, substance-induced mood disorder, mood disorder not otherwise specified; generalized anxiety disorder, obsessive-compulsive disorder, panic disorder, acute stress disorder, post-traumatic stress disorder; mental retardation; pervasive developmental disorders; attention deficit disorders, attention-deficit/hyperactivity disorder, disruptive behaviour disorders; personality disorder of the paranoid type, personality disorder of the schizoid type, personality disorder of the schizotypical type; tic disorders, Tourette's syndrome; substance dependence; substance abuse; substance withdrawal; trichotillomania.

To optimize treatment of patients suffering from a disorder as mentioned in the foregoing paragraph, the compounds of Formula (I) may be administered together with other psychotropic compounds. Thus, in the case of schizophrenia, negative and cognitive symptoms may be targeted.

The present invention also provides a method of treating warm-blooded animals suffering from such disorders, said method comprising the systemic administration of a therapeutic amount of a compound of Formula (I) effective in treating the above described disorders.

The present invention also relates to the use of compounds of Formula (I) as defined hereinabove for the manufacture of a medicament, in particular an antipsychotic medicament, more especially a medicine in the treatment or prevention of schizophrenia, schizophreniform disorder, schizoaffective disorder, delusional disorder, brief psychotic disorder, shared psychotic disorder, psychotic disorder due to a general medical condition, substance-induced psychotic disorder, psychotic disorder not otherwise specified; psychosis associated with dementia; major depressive disorder, dysthymic disorder, premenstrual dysphoric disorder, depressive disorder not otherwise specified, Bipolar I disorder, bipolar II disorder, cyclothymic disorder, bipolar disorder not otherwise specified, mood disorder due to a general medical condition, substance-induced mood disorder, mood disorder not otherwise specified; generalized anxiety disorder, obsessive-compulsive disorder, panic disorder, acute stress disorder, post-traumatic stress disorder; mental retardation; pervasive developmental disorders; attention deficit disorders, attention-deficit/hyperactivity disorder, disruptive behaviour disorders; personality disorder of the paranoid type, personality disorder of the schizoid type, personality disorder of the schizotypical type; tic disorders, Tourette's syndrome; substance dependence; substance abuse; substance withdrawal; trichotillomania.

Those of skill in the treatment of such diseases could determine the effective therapeutic daily amount from the test results presented hereinafter. An effective therapeutic daily amount would be from about 0.01 mg/kg to about 10 mg/kg body weight, more preferably from about 0.05 mg/kg to about 1 mg/kg body weight.

The invention also relates to a pharmaceutical composition comprising a pharmaceutically acceptable carrier and, as active ingredient, a therapeutically effective amount of a compound according to Formula (I).

For ease of administration, the subject compounds may be formulated into various pharmaceutical forms for administration purposes. The compounds according to the invention, in particular the compounds according to Formula (I), a pharmaceutically acceptable acid or base addition salt thereof, a stereochemically isomeric form thereof, an N-oxide form thereof and a prodrug thereof, or any subgroup or combination thereof may be formulated into various pharmaceutical forms for administration purposes. As appropriate compositions there may be cited all compositions usually employed for systemically administering drugs. To prepare the pharmaceutical compositions of this invention, an effective amount of the particular compound, optionally in addition salt form, as the active ingredient is combined in intimate admixture with a pharmaceutically acceptable carrier, which carrier may take a wide variety of forms depending on the form of preparation desired for administration. These pharmaceutical compositions are desirable in unitary dosage form suitable, in particular, for administration orally, rectally, percutaneously, by parenteral injection or by inhalation. For example, in preparing the compositions in oral dosage form, any of the usual pharmaceutical media may be employed such as, for example, water, glycols, oils, alcohols and the like in the case of oral liquid preparations such as suspensions, syrups, elixirs, emulsions and solutions; or solid carriers such as starches, sugars, kaolin, diluents, lubricants, binders, disintegrating agents and the like in the case of powders, pills, capsules and tablets. Because of their ease in administration, tablets and capsules represent the most advantageous oral dosage unit forms in which case solid pharmaceutical carriers are obviously employed. For parenteral compositions, the carrier will usually comprise sterile water, at least in large part, though other ingredients, for example, to aid solubility, may be included. Injectable solutions, for example, may be prepared in which the carrier comprises saline solution, glucose solution or a mixture of saline and glucose solution. Injectable solutions, for example, may be prepared in which the carrier comprises saline solution, glucose solution or a mixture of saline and glucose solution. Injectable solutions containing compounds of Formula (I) may be formulated in an oil for prolonged action. Appropriate oils for this purpose are, for example, peanut oil, sesame oil, cottonseed oil, corn oil, soybean oil, synthetic glycerol esters of long chain fatty acids and mixtures of these and other oils. Injectable suspensions may also be prepared in which case appropriate liquid carriers, suspending agents and the like may be employed. Also included are solid form preparations that are intended to be converted, shortly before use, to liquid form preparations. In the compositions suitable for percutaneous administration, the carrier optionally comprises a penetration enhancing agent and/or a suitable wetting agent, optionally combined with suitable additives of any nature in minor proportions, which additives do not introduce a significant deleterious effect on the skin. Said additives may facilitate the administration to the skin and/or may be helpful for preparing the desired compositions. These compositions may be administered in various ways, e.g., as a transdermal patch, as a spot-on, as an ointment. Acid or base addition salts of compounds of Formula (I) due to their increased water solubility over the corresponding base or acid form, are more suitable in the preparation of aqueous compositions.

It is especially advantageous to formulate the aforementioned pharmaceutical compositions in unit dosage form for ease of administration and uniformity of dosage. Unit dosage form as used herein refers to physically discrete units suitable as unitary dosages, each unit containing a predetermined quantity of active ingredient calculated to produce the desired therapeutic effect in association with the required pharmaceutical carrier. Examples of such unit dosage forms are tablets (including scored or coated tablets), capsules, pills, powder packets, wafers, suppositories, injectable solutions or suspensions and the like, and segregated multiples thereof.

Since the compounds according to the invention are potent orally administrable compounds, pharmaceutical compositions comprising said compounds for administration orally are especially advantageous.

In order to enhance the solubility and/or the stability of the compounds of Formula (I) in pharmaceutical compositions, it can be advantageous to employ α-, β- or γ-cyclodextrins or their derivatives, in particular hydroxyalkyl substituted cyclodextrins, e.g. 2-hydroxypropyl-β-cyclodextrin. Also co-solvents such as alcohols may improve the solubility and/or the stability of the compounds according to the invention in pharmaceutical compositions.

Preparation

Compounds of Formula (I) wherein R, R¹, R² and R³ are as defined before and X is nitrogen could be prepared by reacting a compound of Formula (II),

wherein R² and R³ are as defined before and X is nitrogen, with a reagent of Formula R¹—CHY—R (III-a), where R and R¹ are as defined before and Y represents a leaving group such as halo, e.g. chloro, bromo or iodo, or a sulfonyloxy group, e.g. methylsulfonyloxy, trifluoromethylsulfonyloxy, or methylphenylsulfonyloxy in the presence of a base such as diisopropylethylamine or polymer supported 1,5,7-triazabicyclo[4.4.0]dec-5-ene, in a suitable solvent such as acetonitrile and under suitable reaction conditions, such as a convenient temperature, either by conventional heating or under microwave irradiation for a period of time to ensure the completion of the reaction.

Alternatively, the compounds of Formula (I) wherein R, R¹, R² and R³ are as defined before and X is nitrogen could be prepared by reacting a compound of Formula (II) wherein R² and R³ are as defined before and X is nitrogen, by reductive N-alkylation with a reagent of Formula R¹—C(═O)—R (III-b), where R and R¹ are as defined before, in the presence of a suitable reducing agent such as sodium triacetoxyborohydride or polymer supported triacetoxyborohydride, a suitable acid catalyst, such as acetic acid, in a suitable reaction inert solvent such as dichloromethane, 1,2-dichloroethane or N,N-dimethylformamide.

Compounds of Formula (II) wherein R² and R³ are as defined before and X is nitrogen, may be prepared by deprotection of the protecting group in an intermediate of Formula (IV)

where L represents a suitable protecting group, such as a benzyloxycarbonyl, benzyl or tert-butoxycarbonyl, R² and R³ are as defined before and X is nitrogen, under suitable conditions, such as hydrochloric acid when L represents a benzyloxycarbonyl group, trifluoroacetic acid in dichloromethane when L represents a tert-butoxycarbonyl group or reaction with 1-chloroethyl-chloroformate, in the presence of a suitable base, such as diisopropylethylamine, in dichloromethane, when L represents a benzyl group.

Compounds of Formula (IV), wherein R² and R³ are as defined before and X is nitrogen and L represents a suitable protecting group, may be prepared by reacting a compound of Formula (V),

where R² is as defined before and L represents a suitable protecting group, such as benzyloxycarbonyl, benzyl or tert-butoxycarbonyl, with a 5-chloro-[1,3,4]thiadiazole of Formula (VI)

wherein R³ is as defined before and X is nitrogen, in the presence of a base such as diisopropylethylamine, in a suitable solvent such as acetonitrile and under suitable reaction conditions, such as a convenient temperature, either by conventional heating or under microwave irradiation for a period of time to ensure the completion of the reaction.

A 5-chloro-[1,3,4]thiadiazole of Formula (VI) wherein R³ is trifluoromethyl and X is nitrogen can be prepared by procedures similar to those described in DE 82/3218482.

A 5-chloro-[1,3,4]thiadiazole of Formula (VI) wherein R³ is cyano and X is nitrogen can be prepared by procedures similar to those described in U.S. Pat. No. 5,736,545.

Compounds of Formula (I) wherein R, R¹, R² and R³ are as defined before and X is nitrogen can also be prepared by reacting a 5-chloro-[1,3,4]thiadiazole of Formula (VI) wherein R³ is trifluoromethyl or cyano and X is nitrogen, with a piperidine derivative of Formula (VII)

where R, R¹ and R² are as defined before, in the presence of a suitable base such as diisopropyethylamine, in a suitable solvent such as acetonitrile, and under suitable reaction conditions, such as a convenient temperature, either by conventional heating or under microwave irradiation for a period of time to ensure the completion of the reaction.

Compounds of Formula (VII), where R and R¹ are as defined before and R²═H, may be prepared by reacting piperidin-4-ylcarbamic acid tent-butyl ester (VIII)

with a reagent of Formula R¹—CHY—R (III-a), where R and R¹ are as defined before and Y represents a leaving group such as halo, e.g. chloro, bromo or iodo, or a sulfonyloxy group, e.g. methylsulfonyloxy, trifluoromethylsulfonyloxy, or methylphenylsulfonyloxy in the presence of a base such as diisopropylethylamine, in a suitable solvent such as such as dichloromethane, followed by deprotection of the tert-butyloxycarbonyl group in an intermediate of Formula (IX), by treatment with an acid, such as trifluoroacetic acid, to give a compound of Formula (VII) where R²═H.

Alternatively, the compounds of Formula (VII) wherein where R and R¹ are as defined before could also be prepared by reacting piperidin-4-ylcarbamic acid tent-butyl ester, by reductive N-alkylation with a reagent of Formula R¹—C(═O)—R (III-b), where R and R¹ are as defined before, in the presence of a suitable reducing agent such as sodium triacetoxyborohydride, a suitable acid catalyst, such as acetic acid, in a suitable reaction inert solvent such as 1,2-dichloroethane, followed by deprotection of the tert-butyloxycarbonyl group in an intermediate of Formula (IX), by treatment with an acid, such as trifluoroacetic acid, to give a compound of Formula (VII) where R²═H.

Compounds of Formula (VII), where R² is C₁₋₄alkyl, could be prepared by reacting a compound of Formula (X)

where R and R¹ are as defined before, with a C₁₋₄alkylamine of Formula R²—NH₂ (XI), in the presence of a suitable reducing agent, such as hydrogen, a suitable catalyst, such as palladium on carbon and in a suitable inert reaction solvent, such as ethanol.

Compounds of Formula (X), where R and R¹ are as defined before, may be prepared by reacting 4,4-ethylenedioxypiperidine (XII)

with a reagent of Formula R¹—C(═O)—R (III-b), where R and R¹ are as defined before, in the presence of a suitable reducing agent such as sodium triacetoxyborohydride, a suitable acid catalyst, such as acetic acid, in a suitable reaction inert solvent such as 1,2-dichloroethane, followed by deprotection of an intermediate of Formula (XIII)

where R and R¹ are as defined before, by treatment with an acid, such as hydrochloric acid.

Compounds of Formula (I) wherein R, R¹, R² and R⁴ are as defined before, R³ is hydrogen and X is carbon and R⁴ is trifluoromethyl could be prepared by reacting a compound of Formula (II),

wherein R² and R⁴ is as defined before, R³ is hydrogen and X is carbon, with a reagent of Formula R¹—CHY—R (III-a), where R and R¹ are as defined before and Y represents a leaving group such as halo, e.g. chloro, bromo or iodo, or a sulfonyloxy group, e.g. methylsulfonyloxy, trifluoromethylsulfonyloxy, or methylphenylsulfonyloxy in the presence of a base such as diisopropylethylamine, in a suitable solvent such as acetonitrile and under suitable reaction conditions, such as a convenient temperature, either by conventional heating or under microwave irradiation for a period of time to ensure the completion of the reaction.

Alternatively, the compounds of Formula (I) wherein R, R¹, R² and R⁴ are as defined before, R³ is hydrogen and X is carbon, could be prepared by reacting a compound of Formula (II) wherein R² and R⁴ are as defined before, R³ is hydrogen and X is carbon, by reductive N-alkylation with a reagent of Formula R¹—C(═O)—R (III-b), where R and R¹ are as defined before, in the presence of a suitable reducing agent such as sodium triacetoxyborohydride, a suitable acid catalyst, such as acetic acid, in a suitable reaction inert solvent such as 1,2-dichloroethane.

Compounds of Formula (II), where R² and R⁴ are as defined before, R³ is hydrogen and X is carbon, may be prepared by deprotection of the protecting group in an intermediate of Formula (IV)

where R² and R⁴ are as defined before, R³ is hydrogen, X is carbon and L represents a suitable protecting group, such benzyl under suitable conditions, such as reaction with 1-chloroethyl-chloroformate, in the presence of a suitable base, such as diisopropylethylamine, in dichloromethane.

Compounds of Formula (IV), wherein R² and R⁴ are as defined before, R³ is hydrogen, X is carbon and L represents a suitable protecting group, could be prepared by reacting a (piperidin-4-yl)-thiourea of Formula (XIV),

wherein R² is as defined before and L represents a suitable protecting group, with 3-bromo-acetone derivative of Formula Br—CH₂—C(═O)—CH₂—R⁴ (XV) in a suitable solvent such as ethanol and under suitable reaction conditions, such as a convenient temperature, either by conventional heating or under microwave irradiation for a period of time to ensure the completion of the reaction.

A (piperidin-4-yl)-thiourea of Formula (XIV) where R² is as defined before and L represents a suitable protecting group can be prepared by procedures similar to those described in WO 03/062215.

Alternatively the compounds of Formula (I) wherein R, R¹, R² and R⁴ are as defined before, R³ is hydrogen and X is carbon, were prepared by reacting a compound of Formula (XVI)

wherein R, R¹ and R² are as defined before, with a 3-bromo-acetone derivative of Formula Br—CH₂—C(═O)—CH₂—R⁴ (XV) in a suitable solvent such as ethanol, either by conventional heating or by microwave irradiation for a period of time sufficient to ensure the completion of the reaction.

Compounds of Formula (XVI) wherein R, R¹ and R² are as defined before may be prepared from a piperidine of Formula (VII) by procedures similar to those described in WO 03/062215.

Experimental Part

Chemistry

Microwave assisted reactions were performed in a single-mode reactor: Emrys™ Optimizer microwave reactor (Personal Chemistry A.B., currently Biotage). Description of the instrument can be found in www.personalchemistry.com.

¹H spectra were recorded on a Bruker, DPX 400 or a Bruker AV-500 spectrometers. The chemical shifts are expressed in ppm relative to tetramethylsilane.

Melting point determinations were performed on a Mettler FP62 apparatus.

The HPLC gradient was supplied by a HP 1100 from Agilent Technologies comprising a quaternary pump with degasser, an autosampler, a column oven (set at 40° C. except for Method 4 where temperature was set at 60° C.), a diode-array detector (DAD) and a column as specified in the respective methods below. Flow from the column was split to a MS detector. The MS detector was configured with an electrospray ionization source. Nitrogen was used as the nebulizer gas. The source temperature was maintained at 140° C. Data acquisition was performed with MassLynx-Openlynx software.

Method 1

In addition to the general procedure: Reversed phase HPLC was carried out on an ACE-C18 column (3.0 μm, 4.6×30 mm) from Advanced Chromatography Technologies, with a flow rate of 1.5 ml/min, at 40° C. The gradient conditions used are: 80% A (0.5 g/l ammonium acetate solution), 10% B (acetonitrile), 10% C (methanol) to 50% B and 50% C in 6.5 minutes, to 100% B at 7 minutes and equilibrated to initial conditions at 7.5 minutes until 9.0 minutes. Injection volume 5 μl. High-resolution mass spectra (Time of Flight, TOF) were acquired only in positive ionization mode by scanning from 100 to 750 in 0.5 seconds using a dwell time of 0.1 seconds. The capillary needle voltage was 2.5 kV for positive ionization mode and the cone voltage was 20 V. Leucine-Enkephaline was the standard substance used for the lock mass calibration.

Method 2

In addition to the general procedure: Reversed phase HPLC was carried out on an ACE-C18 column (3.0 μm, 4.6×30 mm) from Advanced Chromatography Technologies, with a flow rate of 1.5 ml/min, at 40° C. The gradient conditions used are: 80% A (0.5 g/l ammonium acetate solution), 10% B (acetonitrile), 10% C (methanol) to 50% B and 50% C in 6.5 minutes, to 100% B at 7 minutes and equilibrated to initial conditions at 7.5 minutes until 9.0 minutes. Injection volume 5 μl. Low-resolution mass spectra (ZQ detector; quadrupole) were acquired by scanning from 100 to 1000 in 1.0 second using a dwell time of 0.3 seconds. The capillary needle voltage was 3 kV. The cone voltage was 20 V and 50 V for positive ionization mode and 20 V for negative ionization mode.

Method 3

In addition to the general procedure: Reversed phase HPLC was carried out on an XDB-C18 cartridge (1.8 μm, 2.1×30 mm) from Agilent, with a flow rate of 1 ml/min, at 60° C. The gradient conditions used are: 90% A (0.5 g/l ammonium acetate solution), 5% B (acetonitrile), 5% C (methanol) to 50% B and 50% C in 6.5 minutes, to 100% B at 7 minutes and equilibrated to initial conditions at 7.5 minutes until 9.0 minutes. Injection volume 2 μl. High-resolution mass spectra (Time of Flight, TOF) were acquired only in positive ionization mode by scanning from 100 to 750 in 0.5 seconds using a dwell time of 0.1 seconds. The capillary needle voltage was 2.5 kV and the cone voltage was 20 V. Leucine-Enkephaline was the standard substance used for the lock mass calibration.

Method 4

Same as Method 1 using 10 μl of injection volume.

Description 1

4-[Methyl-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amino]-piperidine-1-carboxylic acid benzyl ester (D1)

A mixture of 2-chloro-5-trifluoromethyl-[1,3,4]thiadiazole (0.70 g, 3.72 mmol) (prepared by a procedure similar to that described in DE 82/3218482), 4-methylamino-piperidine-1-carboxylic acid benzyl ester hydrochloride (1.06 g, 3.72 mmol) and diisopropylethylamine (1.60 ml, 9.30 mmol) in acetonitrile (10 ml) was stirred at 120° C. for 30 min., under microwave irradiation. After cooling to room temperature, the reaction mixture was diluted with dichloromethane and extracted with a 10% solution of ammonium chloride (25 ml). The organic layer was separated, dried (Na₂SO₄) and the solvent evaporated in vacuo. The crude product was purified by short open column chromatography (silica gel; 0-0.5% ammonia in methanol (7M)/dichloromethane). The desired fractions were collected and evaporated in vacuo to yield D1 (0.91 g, 62%) as a solid. C₁₇H₁₉F₃N₄O₂S requires 400. Found 401 (MH⁺).

Description 2

Methyl-piperidin-4-yl-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (D2)

A solution of 4-[M ethyl-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amino]-piperidine-1-carboxylic acid benzyl ester (D1) (0.91 g, 2.27 mmol) in a solution 6 N of hydrochloric acid (15 ml) was stirred at 150° C. for 10 min., under microwave irradiation. After cooling to room temperature, the reaction mixture was diluted with water and extracted with dichloromethane (25 ml). The aqueous layer was basified with a saturated solution of sodium carbonate and extracted with dichloromethane (3×25 ml). The combined organic extracts were dried (Na₂SO₄) and the solvent evaporated in vacuo to yield D2 (0.56 g, 93%) as a solid. C₉H₁₃F₃N₄S requires 266. Found 266 (MH⁺).

¹H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.67-1.80 (m, 2H) 1.86 (s, 2H) 2.74 (td, J=12.13, 2.28 Hz, 2H) 3.08 (s, 3H) 3.16-3.26 (m, 2H) 4.01-4.15 (m, 1H).

Description 3

(1-Benzyl-piperidin-4-yl)-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (D3)

A mixture of 2-chloro-5-trifluoromethyl-[1,3,4]thiadiazole (0.42 g, 2.24 mmol) (prepared by a procedure similar to that described in DE 82/3218482), 4-aminomethyl-1-benzylpiperidine (0.4 ml, 1.95 mmol) and diisopropylethylamine (0.5 ml, 2.90 mmol) in acetonitrile (6 ml) was stirred at 120° C. for 15 min., under microwave irradiation. After cooling to room temperature, the reaction mixture was diluted with dichloromethane and extracted with a 10% solution of ammonium chloride (25 ml). The organic layer was separated, dried (Na₂SO₄) and the solvent evaporated in vacuo. The crude product was purified by short open column chromatography (silica gel; 0-0.5% ammonia in methanol (7M)/dichloromethane). The desired fractions were collected and evaporated in vacuo to yield D3 (0.368 g, 48%) as a solid. C₁₅H₁₇F₃N₄S requires 342. Found 343 (MH⁺).

¹H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.62-1.71 (m, 2H) 2.05-2.24 (m, 4 H) 2.85 (s, 2H) 3.40-3.51 (m, 1H) 3.53 (s, 2H) 5.83 (d, J=6.63 Hz, 1H) 7.22-7.36 (m, 5H)

Description 4

Piperidin-4-yl-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (D4)

To a stirred solution of (1-benzyl-piperidin-4-yl)-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (D3) (0.50 g, 1.46 mmol) and diisopropylethylamine (0.76 ml, 4.38 mmol) in dichloromethane (20 ml) at 0° C., was added 1-chloroethyl chloroformate (0.47 ml, 4.38 mmol). The reaction mixture was stirred at room temperature for 2 h. and after this period, the solvent evaporated in vacuo. The crude product was dissolved in methanol (30 ml) and the reaction mixture was stirred at reflux for 1.5 h. After evaporation of the solvent, the crude product was dissolved in water and extracted with diethyl ether (2×25 ml) and dichloromethane (3×25 ml). The aqueous layer was separated and evaporated in vacuo. The crude product was purified by reverse phase HPLC. The desired fractions were collected and evaporated in vacuo to yield D4 (0.29 g, 79%) as a solid. C₈H₁₁F₃N₄S requires 252. Found 253 (MH⁺).

¹H NMR (400 MHz, DMSO-d₆) δ ppm 1.59-1.73 (m, 2H) 2.04-2.14 (m, 2H) 2.54 (s, 1H) 2.88-2.97 (m, 2H) 3.17-3.25 (m, 2H) 3.88-3.96 (m, 1H) 8.91 (br. s., 1H).

Description 5

4-(5-Cyano-[1,3,4]thiadiazol-2-ylamino)-piperidine-1-carboxylic acid tert-butyl ester (D5)

A mixture of 5-chloro-[1,3,4]thiadiazole-2-carbonitrile (0.5 g, 3.44 mmol) (prepared by a procedure similar to that described in U.S. Pat. No. 5,736,545), and 4-amino-piperidine-1-carboxylic acid tert-butyl ester (0.69 g, 3.44 mmol) and diisopropylethylamine (0.72 ml, 4.13 mmol) in acetonitrile (10 ml) was stirred at 130° C. for 30 min., under microwave irradiation. After this period, the solvent was evaporated in vacuo. The crude product was dissolved in dichloromethane and extracted with a saturated solution of ammonium chloride. The organic layer was separated, dried (Na₂SO₄) and the solvent evaporated in vacuo. The crude product was purified by short open column chromatography (silica gel; 3-5% ammonia in methanol (7M)/dichloromethane). The desired fractions were collected and evaporated in vacuo to yield D5 (0.97 g, 63%) as a white solid. C₁₃H₁₉N₅O₂S requires 309. Found 308 (MH⁺).

Description 6

5-(Piperidin-4-ylamino)-[1,3,4]thiadiazole-2-carbonitrile (D6)

To a stirred solution of 4-(5-cyano-[1,3,4]thiadiazol-2-ylamino)-piperidine-1-carboxylic acid tert-butyl ester (D5) (0.973 g, 3.12 mmol) in dichloromethane (55 ml), at 0° C., was added trifluoroacetic acid (3 ml). The reaction mixture was stirred at 0° C. for 1 h. and at room temperature for 18 h. more. After this period, the reaction mixture was extracted with a saturated solution of sodium carbonate. The aqueous layer was extracted with ethyl acetate (2×25 ml). The organic layer was separated, dried (Na₂SO₄) and the solvent evaporated in vacuo to yield D6 (0.60 g, 92%) as a solid. C₈H₁₁N₃S requires 209. Found 210 (MH⁺).

Description 7

1-(3,4-Difluoro-benzyl)-piperidin-4-ylamine (D7)

A mixture of piperidin-4-ylcarbamic acid tert-butyl ester (5 g, 25.0 mmol), 3,4-difluorobenzyl bromide (4.7 g, 22.7 mmol) and diisoproylethylamine (5.9 ml, 34.0 mmol) in dichloromethane (50 ml) was stirred at room temperature for 2 h. After this period, trifluoroacetic acid (31 ml) was added and the reaction was stirred for a further 2 h. The solvent was evaporated in vacuo and a saturated solution of sodium carbonate was added. The mixture was extracted with dichloromethane and the separated organic layers were dried (Na₂SO₄), filtered, and the solvent evaporated in vacuo to yield D7 (5.2 g, 93%) as a solid. C₁₂H₁₆F₂N₂ requires 226. Found 227 (MH⁺).

Description 8

(1-Benzyl-piperidin-4-yl)-(4-trifluoromethyl-thiazol-2-yl)-amine (D8)

To a stirred solution of (1-benzyl-piperidin-4-yl)-thiourea (0.5 g, 2.0 mmol) (prepared by a procedure similar to that described in WO 03/062215) in ethanol (15 ml) was added 3-bromo-1,1,1-trifluoroacetone (0.22 ml, 2.1 mmol) and the reaction mixture was heated at reflux for 1 h. After evaporation of the solvent, the crude product was crystallized from acetonitrile to yield D8 (0.61 g, 88%) as a white solid. C₁₆H₁₈F₃N₃S.HBr free base requires 341. Found 342 (MH⁺).

Melting point (acetonitrile): 247.9° C.).

¹H NMR (400 MHz, DMSO-d₆) δ ppm 1.56-1.75 (m, 1.5H) 1.92-2.10 (m, 1H) 2.18 (d, J=12.85 Hz, 1.5H) 3.03-3.22 (m, 2H) 3.23-3.47 (m, 2H) 3.70-3.86 (m, 0.75H) 3.95 (br. s., 0.25H) 4.29 (d, J=4.98 Hz, 1.5H) 4.34 (d, J=4.98 Hz, 0.5H) 7.35-7.57 (m, 5H) 8.20 (d, J=7.26 Hz, 0.75H) 8.26 (d, J=5.80 Hz, 0.25H) 9.43 (br. s., 0.75H) 9.51 (br. s., 0.25H).

Description 9

Piperidin-4-yl-(4-trifluoromethyl-thiazol-2-yl)-amine (D9)

To a stirred solution of (1-benzyl-piperidin-4-yl)-(4-trifluoromethyl-thiazol-2-yl)-amine (D8) (0.57 g, 1.68 mmol) and diisopropylethylamine (1.04 ml, 5.88 mmol) in dichloromethane (15 ml) at 0° C., was added 1-chloroethyl chloroformate (0.45 ml, 4.2 mmol). The reaction mixture was stirred at room temperature for 3 h. and after this period, diluted with dichloromethane and extracted with a saturated solution of sodium hydrogen carbonate (5 ml). The organic layer was separated, dried (Na₂SO₄) and the solvent evaporated in vacuo. The crude product was dissolved in methanol (5 ml) and the reaction mixture was stirred at reflux for 3 h. After evaporation of the solvent, the crude product was purified by column chromatography (silica gel; 5-8% ammonia in methanol (7M)/dichloromethane). The desired fractions were collected and evaporated in vacuo. The crude product was crystallized from acetonitrile to yield D9 (0.34 g, 81%) as a white solid. C₉H₁₂F₃N₃S requires 251. Found 252 (MH⁺).

Melting point (acetonitrile): 133.0° C.

¹H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.38-1.48 (m, 2H) 2.07-2.14 (m, 2H) 2.69-2.76 (m, 2H) 3.11 (dt, J=13.01, 3.65 Hz, 2H) 3.42-3.51 (m, J=14.36, 6.27, 4.15, 4.04 Hz, 1H) 5.28 (d, J=7.26 Hz, 1H) 6.92 (s, 1H).

EXAMPLE 1 [1-(4-Fluoro-benzyl)-piperidin-4-yl]-methyl-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (E1)

A mixture of methyl-piperidin-4-yl-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (D2) (0.050 g, 0.19 mmol), 4-fluorobenzyl chloride (0.029 ml, 0.24 mmol) and diisopropylethylamine (0.050 ml, 0.28 mmol) in acetonitrile (3 ml) was stirred at 120° C. for 30 min., under microwave irradiation. After cooling to room temperature, the reaction mixture was diluted with dichloromethane and extracted with a 10% solution of ammonium chloride (25 ml). The organic layer was separated, dried (Na₂SO₄) and the solvent evaporated in vacuo. The crude product was purified by flash column chromatography (silica gel; 0-1.5% ammonia in methanol (7M)/dichloromethane) to yield E1 (0.061 g, 87%) as a solid. C₁₆H₁₈F₄N₄S requires 374. Found 375 (MH⁺).

Melting point: 85.8° C.

¹H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.75-1.93 (m, 4H) 2.11 (dt, J=11.45, 3.21 Hz, 2H) 2.98 (s, 2H) 3.07 (s, 3H) 3.49 (s, 2H) 3.91-4.08 (m, 1H) 6.95-7.06 (m, 2H) 7.22-7.33 (m, 3H).

EXAMPLE 2 [1-(3-Fluoro-benzyl)-piperidin-4-yl]-methyl-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (E2)

A mixture of methyl-piperidin-4-yl-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (D2) (0.050 g, 0.19 mmol), 3-fluorobenzyl bromide (0.030 ml, 0.24 mmol) and diisopropylethylamine (0.050 ml, 0.28 mmol) in acetonitrile (3 ml) was stirred at 100° C. for 5 min., under microwave irradiation. After cooling to room temperature, the reaction mixture was diluted with dichloromethane and extracted with a 10% solution of ammonium chloride (25 ml). The organic layer was separated, dried (Na₂SO₄) and the solvent evaporated in vacuo. The crude product was purified by flash column chromatography (silica gel; 0-1.5% ammonia in methanol (7M)/dichloromethane) to yield E2 (0.062 g, 88%) as a solid. C₁₆H₁₈F₄N₄S requires 374. Found 375 (MH⁺).

Melting point: 80.5° C.

¹H NMR (400 MHz, DMSO-d₆) δ ppm 1.73 (s, 2H) 1.86 (dq, J=12.02, 3.73 Hz, 2H) 2.09 (td, J=11.71, 2.07 Hz, 2H) 2.84-2.96 (m, 2H) 3.07 (s, 3H) 3.52 (s, 2H) 3.81-3.94 (m, 1H) 7.04-7.11 (m, 1H) 7.11-7.18 (m, 2H) 7.32-7.42 (m, 1H).

EXAMPLE 4 [1-(4-Fluoro-benzyl)-piperidin-4-yl]-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (E4)

A mixture of piperidin-4-yl-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (D4) (0.040 g, 0.16 mmol), 4-fluorobenzyl chloride (0.023 ml, 0.19 mmol) and diisopropylethylamine (0.042 ml, 0.24 mmol) in acetonitrile (3 ml) was stirred at 120° C. for 30 min., under microwave irradiation. After cooling to room temperature, the reaction mixture was diluted with dichloromethane and extracted with a 10% solution of ammonium chloride (25 ml). The organic layer was separated, dried (Na₂SO₄) and the solvent evaporated in vacuo. The crude product was purified by flash column chromatography (silica gel; 0-3% ammonia in methanol (7M)/dichloromethane) to yield E4 (0.042 g, 73%) as a solid. C₁₅H₁₆F₄N₄S requires 360. Found 361 (MH⁺).

¹H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.61-1.74 (m, 2H) 2.05-2.14 (m, 2H) 2.19 (s, 2H) 2.80-2.89 (m, 2H) 3.38-3.48 (m, 1H) 3.50 (s, 2H) 6.39 (br. s., 1H) 6.97-7.05 (m, 2H) 7.24-7.31 (m, 2H).

EXAMPLE 5 [1-(3,4-Difluoro-benzyl)-piperidin-4-yl]-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (E5)

A mixture of piperidin-4-yl-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (D4) (0.040 g, 0.16 mmol), 3,4-difluorobenzyl bromide (0.024 ml, 0.19 mmol) and diisopropylethylamine (0.042 ml, 0.24 mmol) in acetonitrile (3 ml) was stirred at 100° C. for 5 min., under microwave irradiation. After cooling to room temperature, the reaction mixture was diluted with dichloromethane and extracted with a 10% solution of ammonium chloride (25 ml). The organic layer was separated, dried (Na₂SO₄) and the solvent evaporated in vacuo. The crude product was purified by flash column chromatography (silica gel; 0-3% ammonia in methanol (7M)/dichloromethane) to yield E5 (0.048 g, 80%) as a solid. C₁₅H₁₅F₅N₄S requires 378. Found 379 (MH⁺).

¹H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.61-1.76 (m, 2H) 2.06-2.14 (m, 2H) 2.19 (t, J=11.09 Hz, 2H) 2.78-2.87 (m, 2H) 3.37-3.46 (m, 1H) 3.47 (s, 2H) 6.66 (d, J=5.18 Hz, 1H) 6.98-7.04 (m, 1H) 7.05-7.13 (m, 1H) 7.17 (ddd, J=11.20, 7.88, 2.07 Hz, 1H).

EXAMPLE 9 [1-(3-Fluoro-4-methyl-benzyl)-piperidin-4-yl]-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (E9)

A mixture of piperidin-4-yl-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (D4) (0.025 g, 0.1 mmol), 3-fluoro-4-methylbenzyl bromide (0.012 ml, 0.11 mmol) and polymer supported 1,5,7-triazabicyclo[4.4.0]dec-5-ene (2.9 mmol/g) (0.102 g, 0.30 mmol) in acetonitrile (3 ml) was stirred at 80° C. for 30 min. After cooling to room temperature, the reaction mixture was filtered through an Isolute SCX-2 cartridge. The cartridge was then washed with methanol. The crude product was eluted with a 7M solution of ammonia in methanol. The solvent was evaporated in vacuo. The crude product was purified by flash column chromatography (silica gel; 5% ammonia in methanol (7M)/dichloromethane) to yield E9 (0.017 g, 45%) as a solid. C₁₆H₁₈F₄N₄S requires 374. Found 375 (MH⁺).

¹H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.59-1.74 (m, 2H) 2.05-2.22 (m, 4H) 2.26 (d, J=1.45 Hz, 3H) 2.75-2.89 (m, 2H) 3.38-3.49 (m, 1H) 3.48 (s, 2H) 6.17 (d, J=5.60 Hz, 1H) 6.93-7.02 (m, 2H) 7.11 (t, J=7.77 Hz, 1H).

EXAMPLE 10 1-(3-Fluoro-4-trifluoromethyl-benzyl)-piperidin-4-yl]-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (E10)

A mixture of piperidin-4-yl-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (D4) (0.040 g, 0.16 mmol), 3-fluoro-4-(trifluoromethyl)benzaldehyde (0.038 ml, 0.32 mmol), polymer supported triacetoxyborohydride (2.07 mmol/g) (0.197 g, 0.95 mmol) and acetic acid (0.050 ml) in dichloromethane (2 ml) was shaken at room temperature for 16 h. After this period, the reaction mixture was filtered through an Isolute SCX-2 cartridge. The cartridge was washed with methanol. The crude product was eluted with a 7M solution of ammonia in methanol. The solvent was evaporated in vacuo. The crude product was purified by flash column chromatography (silica gel; 5% ammonia in methanol (7M)/dichloromethane) to yield E10 (0.029 g, 43%) as a white solid. C₁₆H₁₅F₇N₄S requires 428. Found 429 (MH⁺).

Melting point: 130.2° C.

¹H NMR (500 MHz, CHLOROFORM-d) δ ppm 1.64-1.76 (m, 2H) 2.07-2.17 (m, 2H) 2.23 (t, J=10.55 Hz, 2H) 2.74-2.89 (m, 2H) 3.41-3.53 (m, 1H) 3.56 (s, 2H) 6.40 (br. s., 1H) 7.16-7.25 (m, 2H) 7.54 (t, J=7.66 Hz, 1H).

EXAMPLE 13 [1-(3-Trifluoromethoxy-benzyl)-piperidin-4-yl]-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (E13)

A mixture of piperidin-4-yl-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine (D4) (0.025 g, 0.10 mmol), 3-trifluoromethoxy-benzaldehyde (0.034 ml, 0.29 mmol) and polymer supported triacetoxyborohydride (2.07 mmol/g) (0.165 g, 0.29 mmol) in 1,2-dichloroethane (2 ml) was shaken at room temperature for 16 h. After this period, the reaction mixture was filtered through an Isolute SCX-2 cartridge. The cartridge was washed with methanol. The crude product was eluted with a 7M solution of ammonia in methanol. The solvent was evaporated in vacuo. The crude product was purified by flash column chromatography (silica gel; 5% ammonia in methanol (7M)/dichloromethane) to yield E13 (0.029 g, 68%) as a white solid. C₁₆H₁₆F₆N₄OS requires 426. Found 427 (MH⁺).

Melting point: 116.3° C.

¹H NMR (500 MHz, CHLOROFORM-d) δ ppm 1.61-1.70 (m, 2H) 2.09-2.16 (m, 2H) 2.21 (t, J=10.98 Hz, 2H) 2.81-2.87 (m, 2H) 3.46-3.57 (m, 1H) 3.54 (s, 2H) 5.75 (d, J=5.78 Hz, 1H) 7.11 (d, J=8.09 Hz, 1H) 7.23 (dd, 2H) 7.34 (t, J=7.80 Hz, 1H).

EXAMPLE 17 5-[1-(3-Trifluoromethyl-benzyl)-piperidin-4-ylamino]-[1,3,4]thiadiazole-2-carbonitrile (E17)

A mixture of 5-(piperidin-4-ylamino)-[1,3,4]thiadiazole-2-carbonitrile (D6) (0.16 g, 0.76 mmol), 3-(trifluoromethyl)benzaldehyde (0.152 ml, 1.14 mmol) and sodium triacetoxyborohydride (0.24 g, 0.95 mmol) in N,N-dimethylformamide (3 ml) was stirred at room temperature for 16 h. After this period, the reaction mixture was diluted with ethyl acetate and extracted with a saturated solution of sodium carbonate (25 ml). The organic layer was separated, dried (Na₂SO₄) and the solvent evaporated in vacuo. The crude product was purified by flash column chromatography (silica gel; 1-4% ammonia in methanol (7M)/dichloromethane) to yield E17 (0.025 g, 9%) as a white solid. C₁₆H₁₆F₃N₅S requires 367. Found 368 (MH⁺).

¹H NMR (500 MHz, CHLOROFORM-d) δ ppm 1.68-1.80 (m, 2H) 2.06-2.15 (m, 2H) 2.22 (t, J=10.69 Hz, 2H) 2.82-2.92 (m, 2H) 3.32-3.45 (m, 1H) 3.58 (s, 2H) 7.45 (t, J=7.66 Hz, 1H) 7.49-7.55 (m, 2H) 7.59 (s, 1H) 7.61-7.68 (m, 1H).

EXAMPLE 18 5-[1-(3-Fluoro-5-trifluoromethyl-benzyl)-piperidin-4-ylamino]-[1,3,4]thiadiazole-2-carbonitrile (E18)

A mixture of 5-(piperidin-4-ylamino)-[1,3,4]thiadiazole-2-carbonitrile (D6) (0.16 g, 0.76 mmol), 3-fluoro-5-(trifluoromethyl)benzyl bromide (0.124 ml, 0.76 mmol) and diisopropylethylamine (0.20 ml, 1.14 mmol) in acetonitrile (2 ml) and N,N-dimethylformamide (0.5 ml) was stirred at room temperature for 48 h. After this period, the reaction mixture was diluted with dichloromethane and extracted with a saturated solution of ammonium chloride (25 ml). The organic layer was separated, dried (Na₂SO₄) and the solvent evaporated in vacuo. The crude product was purified by flash column chromatography (silica gel; 2-3% ammonia in methanol (7M)/dichloromethane) to yield E18 (0.019 g, 7%) as a solid. C₁₆H₁₅F₄N₅S requires 385. Found 386 (MH⁺).

¹H NMR (500 MHz, CHLOROFORM-d) δ ppm 1.57-1.70 (m, 2H) 2.07-2.15 (m, 2H) 2.22 (t, J=11.13 Hz, 2H) 2.81-2.93 (m, 2H) 3.19 (br. s., 1H) 3.58 (s, 2H) 3.64-3.73 (m, 1H) 7.24 (d, J=8.09 Hz, 1H) 7.28 (d, J=8.96 Hz, 1H) 7.40 (s, 1H).

EXAMPLE 19 5-[1-(3,4-Difluoro-benzyl)-piperidin-4-ylamino]-[1,3,4]thiadiazole-2-carbonitrile (E19)

A mixture of 5-chloro-[1,3,4]thiadiazole-2-carbonitrile (0.3 g, 2.06 mmol) (D6) (prepared by a procedure similar to that described in U.S. Pat. No. 5,736,545), 1-(3,4-difluoro-benzyl)-piperidin-4-ylamine (D7) (0.47 g, 2.06 mmol) and diisopropylethylamine (0.54 ml, 3.09 mmol) in acetonitrile (5 ml) in a sealed tube, was stirred at 80° C. for 1 h., under microwave irradiation. After this period, the reaction mixture was diluted with dichloromethane and extracted with a saturated solution of sodium carbonate (25 ml). The organic layer was separated, dried (Na₂SO₄) and the solvent evaporated in vacuo. The crude product was purified by short open column chromatography (silica gel; 0-2.5% ammonia in methanol (7M)/dichloromethane). The desired fractions were collected and evaporated in vacuo. The crude product was precipitated from acetonitrile to yield E19 (0.17 g, 25%) as a solid. C₁₅H₁₅F₂N₅S requires 335. Found 336 (MH⁺).

Melting point (acetonitrile): 199.4° C.

¹H NMR (500 MHz, CHLOROFORM-d) δ ppm 1.64-1.83 (m, 2H) 2.15 (d, J=11.85 Hz, 2H) 2.24 (t, J=10.11 Hz, 2H) 2.89 (d, J=10.98 Hz, 2H) 3.46-3.58 (m, 3H) 6.74 (br. s., 1H) 7.02-7.08 (m, 1H) 7.09-7.16 (m, 1H) 7.22 (t, J=9.25 Hz, 1H).

EXAMPLE 21 5-[1-(3,4,5-Trifluoro-benzyl)-piperidin-4-ylamino]-[1,3,4]thiadiazole-2-carbonitrile (E21)

A mixture of 5-chloro-[1,3,4]thiadiazole-2-carbonitrile (0.3 g, 2.06 mmol) (D6) (prepared by a procedure similar to that described in U.S. Pat. No. 5,736,545), 1-(3,4,5-Trifluoro-benzyl)-piperidin-4-ylamine [prepared by a procedure similar to that described for (D7)] (0.50 g, 2.06 mmol) and diisopropylethylamine (0.54 ml, 3.09 mmol) in acetonitrile (5 ml) in a sealed tube, was stirred at 80° C. for 1 h., under microwave irradiation. After this period, the reaction mixture was diluted with dichloromethane and extracted with a saturated solution of sodium carbonate (25 ml). The organic layer was separated, dried (Na₂SO₄) and the solvent evaporated in vacuo. The crude product was purified by short open column chromatography (silica gel; 0-2.5% ammonia in methanol (7M)/dichloromethane). The desired fractions were collected and evaporated in vacuo. The crude product was precipitated from acetonitrile/diisopropyl ether to yield E21 (0.18 g, 24%) as a solid. C₁₅H₁₄F₃N₅S requires 353. Found 354 (MH⁺).

Melting point (acetonitrile/diisopropyl ether): 211.3° C.

¹H NMR ((500 MHz, DMSO-d₆) δ ppm 1.47-1.59 (m, 2H) 1.98 (d, J=10.69 Hz, 2H) 2.15 (t, J=10.55 Hz, 2H) 2.73 (d, J=11.27 Hz, 2H) 3.48 (s, 2H) 3.64-3.75 (m, 1H) 7.21-7.32 (m, 2H) 8.81 (br. s., 1H).

EXAMPLE 22 [1-(3,4-Difluoro-benzyl)-piperidin-4-yl]-(4-trifluoromethyl-thiazol-2-yl)-amine (E22)

A mixture of piperidin-4-yl-(4-trifluoromethyl-thiazol-2-yl)-amine (D9) (0.050 g, 0.2 mmol), 3,4-difluorobenzyl bromide (0.028 ml, 0.22 mmol) and diisopropylethylamine (0.053 ml, 0.32 mmol) in acetonitrile (1 ml) was stirred at 120° C. for 5 min., under microwave irradiation. The reaction mixture was diluted with dichloromethane and extracted with water. The organic layer was separated, dried (Na₂SO₄) and the solvent evaporated in vacuo. The crude product was purified by column chromatography (silica gel; AcOEt). The desired fractions were collected and evaporated in vacuo. The product thus obtained was dissolved in acetonitrile (0.5 ml) and treated with a solution of hydrochloric acid in diethyl ether (2M) to yield the corresponding hydrochloride salt E22 (0.071 g, 85%) as a white solid. C₁₆H₁₆F₅N₃S.HCl free base requires 377. Found 378 (MH⁺).

Melting point (acetonitrile): 238° C.

¹H NMR (400 MHz, DMSO-d₆) δ ppm 1.78-1.93 (m, 1.5H) 1.95-2.06 (m, 0.5H) 2.13 (m, 2H) 2.97-3.11 (m, 1.5H) 3.11-3.27 (m, 1H) 3.34 (m, 1.5H) 3.69-3.85 (m, 0.75H) 3.90-3.98 (m, 0.25H) 4.25 (d, J=5.18 Hz, 1.5H) 4.30 (d, J=5.39 Hz, 0.5H) 7.36 (d, J=1.24 Hz, 0.75H) 7.41 (d, J=1.04 Hz, 0.25H) 7.43-7.60 (m, 2H) 7.82 (ddd, J=11.51, 7.88, 1.97 Hz, 1H) 8.30 (br. s., 0.75H) 8.48 (d, J=5.60 Hz, 0.25H) 11.03 (br. s., 0.25H) 11.22 (br. s., 0.75H).

Example (E3) was prepared from (D2) and the corresponding alkylating agent, by procedures similar to those described for Example (E2). Examples (E6-E8) were prepared from (D4) and the corresponding alkylating agents, by procedures similar to those described for Example (E5). Examples (E11-E12) were prepared from (D4) and the corresponding aldehydes, by procedures similar to those described for Example (E10). Examples (E14-E16) were prepared from (D4) and the corresponding aldehydes, by procedures similar to those described for Example (E13).

Ex.

R² Melting Point (° C.) Molecular Formula M. Wt Free base MH+ RT (min) LCMS Method E1

Me 85.8 C₁₆H₁₈F₄N₄S 374 375 4.89 1 E2

Me 80.5 C₁₆H₁₈F₄N₄S 374 375 5.02 1 E3

Me 167.4 C₁₆H₁₈F₄N₄S 374 375 4.93 1 E4

H N.D. C₁₅H₁₆F₄N₄S 360 361 4.33 1 E5

H N.D. C₁₅H₁₅F₅N₄S 378 379 4.65 1 E6

H 125.9 C₁₅H₁₅F₅N₄S 378 379 4.81 1 E7

H 124.1 C₁₅H₁₆F₄N₄S 360 361 4.51 1 E8

H 129.4 C₁₅H₁₆F₄N₄S 360 361 4.43 1 E9

H N.D. C₁₆H₁₈F₄N₄S 374 375 4.89 1 E10

H 130.2 C₁₆H₁₅F₇N₄S 428 429 5.22 1 E11

H 121.9 C₁₆H₁₆F₆N₄S 410 411 5.12 1 E12

H 151.8 C₁₆H₁₈ClF₃N₄S 390 391 5.53 1 E13

H 116.3 C₁₆H₁₆F₆N₄OS 426 427 5.34 2 E14

H N.D. C₁₆H₁₆F₃N₅S 367 368 4.24 2 E15

H N.D. C₁₆H₁₆F₃N₅S 367 368 4.23 2 E16

H 118.3 C₁₇H₂₁F₃N₄S 370 371 5.16 2

Examples (E20-E21) were prepared from 5-chloro-[1,3,4]thiadiazole-2-carbonitrile (D6) and the corresponding 1-(benzyl)-piperidin-4-ylamine derivatives, by procedures similar to those described for Example (E19). The corresponding 1-(benzyl)-piperidin-4-ylamine derivatives were prepared from piperidin-4-ylcarbamic acid tent-butyl ester and the corresponding alkylating agents, by procedures similar to those described for Description (D7).

Ex.

Melting Point (° C.) Molecular Formula M. Wt Free base MH+ RT (min) LCMS Method E17

N.D. C₁₆H₁₆F₃N₅S 367 368 4.58 1 E18

N.D. C₁₆H₁₅F₄N₅S 385 386 4.83 1 E19

199.4 C₁₅H₁₅F₂N₅S 335 336 3.91 3 E20

Decomp. C₁₅H₁₅F₂N₅S 335 336 4.20 1 E21

211.3 C₁₅H₁₄F₃N₅S 335 336 4.27 3

The following additional examples (E23-E25) were prepared from (D9) and the corresponding alkylating agents, by procedures similar to those described for Example (E22). Examples (E22-E25) were isolated as hydrochloric acid salt.

Ex.

Melting Point (° C.) Molecular Formula M. Wt Free base MH+ RT (min) LCMS Method E22

238 C₁₆H₁₆F₅N₃S•HCl 377 378 5.01 1 E23

214.2 C₁₆H₁₇F₄N₃S•HCl 359 360 4.70 4 E24

220.5 C₁₆H₁₆F₅N₃S•HCl 377 378 5.16 1 E25

229.2 C₁₇H₁₉F₄N₃S•HCl 373 374 5.08 1 Pharmacology In Vitro Binding Affinity for Human D2_(L) Receptor

Frozen membranes of human Dopamine D2_(L) receptor-transfected CHO cells were thawed, briefly homogenised using an Ultra-Turrax T25 homogeniser and diluted in Tris-HCl assay buffer containing NaCl, CaCl₂, MgCl₂, KCl (50, 120, 2, 1, and 5 mM respectively, adjusted to pH 7.7 with HCl) to an appropriate protein concentration optimised for specific and non-specific binding. Radioligand [³H]Spiperone (NEN, specific activity ˜70 Ci/mmol) was diluted in assay buffer at a concentration of 2 nmol/L. Prepared radioligand (50 μl), along with 50 μl of either the 10% DMSO control, Butaclamol (10⁻⁶ mol/l final concentration), or compound of interest, was then incubated (30 min, 37° C.) with 400 μl of the prepared membrane solution. Membrane-bound activity was filtered through a Packard Filtermate harvester onto GF/B Unifilterplates and washed with ice-cold Tris-HCl buffer (50 mM; pH 7.7; 6×0.5 ml). Filters were allowed to dry before adding scintillation fluid and counting in a Topcount scintillation counter. Percentage specific bound and competition binding curves were calculated using S-Plus software (Insightful). The compounds had a pIC₅₀ value>5.0.

Fast Dissociation

Compounds showing an IC₅₀ less than 10 μM were tested in an indirect assay adapted from a method published by Josee E. Leysen and Walter Gommeren, Journal of Receptor Research, 1984, 4(7), 817-845, to evaluate their rate of dissociation. Compounds at a concentration of 4 times their IC₅₀ were first incubated for one hour with human D2L receptor cell membranes in a volume of 2 ml at 25° C., then filtered over glass-fibre filter under suction using a 40 well multividor. Immediately after, the vacuum was released. 0.4 ml of pre-warmed buffer (25° C.) containing 1 nM [³H]spiperone was added on the filter for 5 minutes. The incubation was stopped by initiating the vacuum and immediate rinsing with 2×5 ml of ice-cold buffer. The filter-bound radioactivity was measured in a liquid scintillation spectrometer. The principle of the assay is based on the assumption that the faster a compound dissociates from the D2 receptor, the faster [³H]spiperone binds to the D2 receptor. For example, when D2 receptors are incubated with clozapine at the concentration of 1850 nM (4×IC₅₀), [³H]spiperone binding is equivalent to 60-70% of its total binding capacity (measured in absence of drug) after 5 min incubation on filter. When incubated with other antipsychotics, [³H]spiperone binding varies between 20 and 50%. Since clozapine was included in each filtration run, tested compounds were considered fast dissociating D2 antagonists if they were dissociating as fast or faster than clozapine. The compounds had a dissociation rate faster than that of clozapine, i.e. >50%. 

The invention claimed is:
 1. A compound of formula (I)

or a pharmaceutically acceptable salt, or a stereoisomeric form thereof, wherein R is hydrogen or C₁₋₆alkyl; R¹ is phenyl; phenyl substituted with 1, 2 or 3 substituents each independently selected from the group consisting of halo, cyano, C₁₋₄alkyl, C₁₋₄alkyloxy, perfluoroC₁₋₄-alkyl, and perfluoroC₁₋₄alkyloxy; thienyl; thienyl substituted with 1 or 2 substituents selected from the group consisting of halo and C₁₋₄alkyl; C₁₋₄alkyl; or C₁₋₄alkyl substituted with hydroxyl, C₃₋₈cycloalkyl or C₅₋₇cycloalkenyl; R² is hydrogen or C₁₋₆alkyl; R³ is hydrogen, trifluoromethyl or cyano; X is N or CR⁴ wherein R⁴ is hydrogen, trifluoromethyl or cyano.
 2. A compound according to claim 1 wherein R is hydrogen; R¹ is phenyl; phenyl substituted with 1, 2 or 3 substituents each independently selected from the group consisting of hydrogen, halo, cyano, C₁₋₄alkyl, C₁₋₄alkyloxy, perfluoroC₁₋₄alkyl, and trifluoromethoxy; thienyl; thienyl substituted with 1 or 2 substituents selected from the group consisting of halo and C₁₋₄alkyl; C₁₋₄alkyl; or C₁₋₄alkyl substituted with hydroxyl, C₃₋₈cycloalkyl or and C₅₋₇cycloalkenyl; R² is hydrogen or methyl; X is nitrogen and R³ is trifluoromethyl.
 3. A compound according to claim 1 wherein R is hydrogen; R¹ is phenyl; phenyl substituted with 1, 2 or 3 substituents each independently selected from the group consisting of hydrogen, halo, cyano, C₁₋₄alkyl, C₁₋₄alkyloxy, perfluoroC₁₋₄alkyl, and trifluoromethoxy; thienyl; thienyl substituted with 1 or 2 substituents selected from the group consisting of halo and C₁₋₄alkyl; C₁₋₄alkyl; or C₁₋₄alkyl substituted with hydroxyl, C₃₋₈cycloalkyl or C₅₋₇cycloalkenyl; R² is hydrogen or methyl; X is nitrogen and R³ is cyano.
 4. A compound according to claim 1 wherein R is hydrogen; R¹ is phenyl; phenyl substituted with 1, 2 or 3 substituents each independently selected from the group consisting of hydrogen, halo, cyano, C₁₋₄alkyl, C₁₋₄alkyloxy, perfluoroC₁₋₄alkyl, and trifluoromethoxy; thienyl; thienyl substituted with 1 or 2 substituents selected from the group consisting of halo and C₁₋₄alkyl; C₁₋₄alkyl; or C₁₋₄alkyl substituted with hydroxyl, C₃₋₈cycloalkyl or C₅₋₇cycloalkenyl; R² is hydrogen or methyl; R³ is hydrogen; and X is CR⁴ wherein R⁴ is trifluoromethyl.
 5. A compound according to claim 1 wherein the compound is selected from the group consisting of [1-(4-Fluoro-benzyl)-piperidin-4-yl]-methyl-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine, [1-(3-Fluoro-benzyl)-piperidin-4-yl]-methyl-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine, [1-(4-Fluoro-benzyl)-piperidin-4-yl]-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine, [1-(3,4-Difluoro-benzyl)-piperidin-4-yl]-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine, [1-(3-Fluoro-4-methyl-benzyl)-piperidin-4-yl]-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine, 1-(3-Fluoro-4-trifluoromethyl-benzyl)-piperidin-4-yl]-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine, [1-(3-Trifluoromethoxy-benzyl)-piperidin-4-yl]-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine, 5-[1-(3-Trifluoromethyl-benzyl)-piperidin-4-ylamino]-[1,3,4]thiadiazole-2-carbonitrile, 5-[1-(3-Fluoro-5-trifluoromethyl-benzyl)-piperidin-4-ylamino]-[1,3,4]thiadiazole-2-carbonitrile, 5-[1-(3,4-Difluoro-benzyl)-piperidin-4-ylamino]-[1,3,4]thiadiazole-2-carbonitrile, 5-[1-(3,4,5-Trifluoro-benzyl)-piperidin-4-ylamino]-[1,3,4]thiadiazole-2-carbonitrile, [1-(3,4-Difluoro-benzyl)-piperidin-4-yl]-(4-trifluoromethyl-thiazol-2-yl)-amine, (1-Benzyl-piperidin-4-yl)-(5-trifluoromethyl-[1,3,4]thiadiazol-2-yl)-amine and (1-Benzyl-piperidin-4-yl)-(4-trifluoromethyl-thiazol-2-yl)-amine.
 6. A pharmaceutical composition comprising a therapeutically effective amount of a compound as defined in claim
 1. 7. A pharmaceutical composition comprising a therapeutically effective amount of a compound as defined in claim
 6. 